CHAPTER VIII. 



EXPOSURE DISCOLOURED BALSAM AN EXPOSURE 

 RECORD EXAMPLES OF EXPOSURE. 



So much depends upon the light, the power of 

 lens and eyepiece used, the colour and opacity of 

 the object, camera extensions, etc., that only an 

 approximate estimate may be made from the 

 results of another worker ; but the exposures 

 tabulated hereafter were obtained with a paraffin 

 lamp having a wick lin. wide. A word of warning 

 may be given concerning specimens mounted in 

 balsam. If one of these show patches of deeper 

 colour in some parts than others, or if the gold 

 size, marine glue, or other material of which the 

 cell is constructed has dissolved and stained its 

 contents, it should be rejected forthwith, for no 

 amount of tinkering will give a good negative. 

 Slides deep yellow on one side and perfectly trans- 

 parent on the other, whilst not unfit for visual 

 examination, are quite unsuitable for photography. 

 This shows that some attention ought to be paid 

 to the quality of the mounting. 



A record of all exposures should be kept, enter- 

 ing the failures as well as the successes ; it should 



